The curing of monomeric materials to produce thermoset resins is well known in the art. In general, the polymerizable monomers have at least one and customarily more than one active group which serves as the reactive site for a curing or crosslinking polymerization to produce the thermoset resins which are typically highly crosslinked. The curing or crosslinking of many if not most thermoset resins, for example, the curing of epoxy resins, requires the use of a curing agent, whether catalytic or stoichiometric, to cause the curing or crosslinking reaction to occur at an acceptable rate. Certain other monomers cure in the absence of added curing agent but only upon application of high intensity energy, e.g., ultraviolet (UV) light. Even in the presence of most curing agents the rate of crosslinking is often unduly slow and the addition of an accelerator is generally required to obtain sufficiently rapid curing.
There are some monomers in which the active sites are such that no added curing agent is required and such monomers cure upon application of heat. Such monomers are termed "self-curing". One class of such monomers includes within the molecular structure one or more moieties of an arylcyclobutene, particularly a benzocyclobutene. Such monomers are suitably cured by reaction with a conventional curing agent but also self-cure upon heating in the absence of a curing agent. Without wishing to be bound by any particular theory, it appears probably that upon application of heat the cyclobutene ring undergoes ring opening to produce active intermediates which crosslink by undergoing reaction with adjacent molecules. The resulting cured thermoset resins have properties of rigidity and strength. A series of U.S. patents to Kirchhoff, illustrated by U.S. Pat. No. 4,540,763, describes the production and curing of a large number of benzocyclobutene derivatives, including ethers of bis(hydroxyphenyl)alkanes, wherein the linking group connecting the phenyl of the bis(hydroxyphenyl)alkane to the benzocyclobutene moiety is attached directly to the six-membered ring of the benzocyclobutene. Such monomers are said to be self-curing. In copending U.S. patent application Ser. No. 349,546, filed May 9, 1989, there is described and claimed a class of benzocyclobutenealkyl ethers of bis(hydroxylphenyl)alkanes having a linking group somewhat different from those of Kirchhoff but also attached to the six-membered ring of the benzocyclobutene moiety. These derivatives are also self-curing. It would be of advantage, however, to provide arylcyclobutene derivatives, particularly benzocyclobutene derivatives, having a different link to the remainder of the molecule, i.e., a link from the 4-membered cyclobutene ring of the arylcyclobutene ring system. The resulting monomers crosslink with or without added curing agent to produce cured thermoset resins having good properties.